Ashlee Simpson is trying to stay ''fit and strong'' during her pregnancy.

The 30-year-old star, who is expecting first child with husband Evan Ross, has been doing Cardio Barre classes two to three times a week in a bid to maintain ''a healthy weight'' as her due date approaches.

Cardio Barre creator Richard Giorla said: ''She wants to stay fit and strong and maintain a healthy weight. Also to feel good. During this pregnancy she wants to be prepared, healthy and fit mentally and physically.

''Cardio Barre is a ballet inspired workout. Ashlee is a beautifully classical trained dancer. Hence her passion for Cardio Barre. The dance inspired ballet techniques are no impact/high energy so they are safe to do while pregnant. The workout gives clients an elevated heart rate and is the ultimate tool in body sculpting, creating a ballet physique.''

Ashlee, who was recently spotted enjoying a well-earned holiday in Los Cabos with Evan, never complains about working out.

Richard told E! News: ''The weight and energy makes it more challenging, but she never complains and always gives her best. She is truly inspirational.''

The 'Boyfriend' hitmaker gained 50 pounds while expecting her six-year-old son, Bronx, with ex-husband Pete Wentz, and previously credited Reebok EasyTone shoes for helping her to get back in shape.

Speaking in 2010, she said: ''When I wanted to get back into shape, I worked out and these shoes are amazing because you can really feel them in your booty. But I also worked out and ate healthy.''